Welcome to the final episode of Simon Schaffer's fascinating documentary series, Light Fantastic. Thanks to the incredible work of Einstein, we know today that although light travels in straight lines through space, space-time itself isn't always all that straight. This fascinating conjecture received its first empirical confirmation in 1919, when Sir Arthur Eddington led an expedition to observe and record a solar eclipse, and then measured the apparent position shift of a few stars behind the sun (the picture to the right demonstrates the basic idea). Einstein became an overnight celebrity.
Before Einstein, however, all investigations concerning light worked under the simple assumption that all light does is reveal the world to us. What we didn't realize until the 18th century, however, through the work of people like Joseph Priestley, was that light has a causal influence on the world, especially the world of living organisms. In a very strange but real sense, the medium that allowed us to see the world was also producing that world...
But the story gets even more interesting. The attempt to investigate the ultimate nature of light would also illuminate (get it?) how the human mind itself works. John Dalton would be the first to discover color blindness (partly through his own unfortunate experience); Benjamin Thompson (or Count Rumford, if you like) would demonstrate the ultimate subjective nature of color through a series of fascinating and bewildering experiments (opening the door for a revolution in the world of art); and Thomas Young would be responsible for a paradigm shift that cast light as a wave, to be understood through principles analogous to those used to describe sound. In the process, he would finally be able to explain the mystery of color as the visual equivalent of musical notes.But that's just part of the story, and as we explore further, we'll see that understanding the nature of light can actually become a matter of life and death...
If you can see the 74 in the picture above, your vision is probably okay. If you don't see it, you've just been diagnosed with color blindness by Doctor Philosophy Monkey :)
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